A Short Review of Experimental Peritoneal Sclerosis: From Mice to Men

Iron increases the profibrotic properties of the senescent peritoneal mesothelial cells

BACKGROUND

Treatment of anemia in peritoneal dialysis patients often requires intravenous iron supplementation. Iron diffuses into the peritoneal cavity and is injurious to the peritoneum. We studied how intermittent exposure to iron changes the properties of the senescent peritoneal mesothelial cells (MC).

METHODS

Replicative senescence was induced in MC in control medium (Con) or in control medium with intermittent exposure to iron isomaltoside 15 µg/dL (Con-IIS). After 10 passages properties of MC from both groups were compared to MC not exposed to replicative senescence.

RESULTS

In senescent MC population doubling time was elongated, intracellular generation of free radicals and staining for β-galactosidase was stronger than in MC not exposed to replicative senescence. All these effects were stronger in MC intermittently exposed to IIS. In these cells intracellular iron content was also higher. Also expression of genes p21 and p53 was stronger in MC intermittently treated with IIS. In senescent cells higher release and expression of IL6 and TGFβ1 was observed and that effect was stronger in MC treated with iron. Senescent MC had reduced fibrinolytic activity, what may predispose to the peritoneal fibrosis. Synthesis of collagen was higher in senescent cells, more in MC treated with iron.

CONCLUSION

MC aging results in change of their genotype and phenotype which lead to their profibrotic effect. Exposure to iron enhances these changes.

Effects of a Phosphodiesterase inhibitor on the Browning of Adipose Tissue in Mice

Cilostazol is a selective inhibitor of phosphodiesterase type 3 (PDE3) that increases intracellular cyclic adenosine monophosphate (cAMP), which plays a critical role in the development of the beige phenotype and the activation of its thermogenic program in white adipose tissue (WAT). We investigated the metabolic effects of PDE3B inhibition with cilostazol treatment in the adipose tissue of high-fat diet (HFD)-fed mice. Seven-week-old male C57BL/6J mice were randomly assigned to either the cilostazol or control group. The control group was divided into two groups: the chow diet and HFD. The expression of uncoupling Protein 1 (UCP1) and other brown adipocyte markers was compared. In the HFD-fed cilostazol group, C57BL/6J mice displayed improvements in systemic metabolism, including improved glucose tolerance and lipid profile, but only modest effects on body weight were observed. In the visceral WAT of HFD-fed cilostazol-treated mice, cAMP/protein kinase A (PKA) signaling pathways were activated, resulting in the “browning” phenotype, smaller fat deposits, and enhanced mRNA expression of UCP1 and other brown adipocyte markers. PDE3B appears to be an important regulator of lipid metabolism, insulin sensitivity, and thermogenic programs in adipose tissues. An increase in intracellular cAMP via PDE3B inhibition with cilostazol treatment promoted the browning of visceral WAT.

Agents that Modulate Peritoneal Membrane Structure and Function

Extensive experience with chronic peritoneal dialysis has identified a series of functional and anatomical pathologic changes in the peritoneal membrane thought to be the result of repeated insults from bioincompatible solutions. Laboratory and clinical findings from recent investigations often conflict and are difficult to interpret due to variations in methodologies, animal models, study designs, and data analyses. The principal pathophysiologic mechanisms identified thus far are oxidative stress, inflammation, and their consequences. Many substances used to neutralize the action of these insults, prevent formation of toxic compounds, or directly alter solute and water transport to improve peritoneal membrane performance have been studied. We herein review the most promising of these substances or those that deserve attention because their use has contributed to better understanding of peritoneal pathophysiology. Most peritoneal solution additives have proved useless due to their toxicity and undesirable effects, ineffectiveness, or manufacturing limitations. A few substances deserve more attention, particularly those capable of restoring negatively charged membrane sites, those that somehow improve permselectivity, scavengers of oxidants, and advanced glycation end-product inhibitors and breakers. Recent publications on clinical experience with neutral pH, low glucose degradation product (GDP) peritoneal solutions, although few and preliminary, are most encouraging. The virtual elimination of GDPs in these novel solutions will probably preclude the need for GDP scavengers and inhibitors. Nonetheless, there is room for further significant improvement in solution biocompatibility and for compounds that may restore peritoneal function.

Intraperitoneal Route of Drug Administration: Should it Be Used in Experimental Animal Studies?

Intraperitoneal (IP) route of drug administration in laboratory animals is a common practice in many in vivo studies of disease models. While this route is an easy to master, quick, suitable for chronic treatments and with low impact of stress on laboratory rodents, there is a common concern that it may not be an acceptable route for drug administration in experimental studies. The latter is likely due to sparsity of information regarding pharmacokinetics of pharmacological agents and the mechanisms through which agents get systemic exposure after IP administration. In this review, we summarize the main mechanisms involved in bioavailability of IP administered drugs and provide examples of pharmacokinetic profiles for small and large molecules in comparison to other routes of administration. We conclude with a notion that IP administration of drugs in experimental studies involving rodents is a justifiable route for pharmacological and proof-of-concept studies where the goal is to evaluate the effect(s) of target engagement rather than properties of a drug formulation and/or its pharmacokinetics for clinical translation.

Generation of Prostate Cancer Patient-Derived Xenografts to Investigate Mechanisms of Novel Treatments and Treatment Resistance

Treatment advances lead to survival benefits of patients with advanced prostate cancer. These treatments are highly efficacious in a subset of patients; however, similarly to other cancers, after initial responses the tumors develop resistance (acquired resistance) and the patients succumb to the disease. Furthermore, there is a subset of patients who do not respond to the treatment at all (de novo resistance). Preclinical testing using patient-derived xenografts (PDXs) has led to successful drug development, and PDXs will continue to provide valuable resources to generate clinically relevant data with translational potential. PDXs demonstrate tumor heterogeneity observed in patients, preserve tumor-microenvironment architecture, and provide clinically relevant treatment responses. In view of the evolving biology of the advanced prostate cancer associated with new treatments, PDXs representing these new tumor phenotypes are urgently needed for the study of treatment responses and resistance. In this chapter, we describe methodologies used to establish prostate cancer PDXs and use of these PDXs to study de novo and acquired resistance.

Case report of encapsulating peritoneal sclerosis: the interpretation of functional and structural peritoneal changes

A case report describing the evolution of encapsulating peritoneal sclerosis is presented to illustrate some of the functional and structural peritoneal membrane changes characteristic of this complication of peritoneal dialysis. The appropriate monitoring of peritoneal transport rates and ultrafiltration, together with attention to clinical signs and symptoms, are essential to the early diagnosis of peritoneal membrane deterioration. Recent reports suggest that timely interventions such as a peritoneal membrane rest period may effectively halt the progression of these functional and structural changes. While the optimal surgical and pharmacological treatment of encapsulating peritoneal sclerosis remains uncertain, the latest literature provides a certain degree of optimism.